This invention generally relates to UV radiation curable acrylate-containing coating compositions, their use in coating articles, such as automotive headlamps, the cured coating or “hardcoats”, and coated articles containing the coatings.
Hardcoats have been used commercially in a variety of applications, such as to protect optical displays. Certain applications, such as automotive headlamps, require that the coatings withstand the rigors of outdoor environments, ideally for the life of the motor vehicle itself. Desirable characteristics for hardcoats include abrasion resistance, good adhesion to the underlying substrate, resistance to microcracks, haze resistance and resistance to yellowing and other forms of discoloration.
Weatherable hardcoats also serve to protect plastics and other substrates that are used outside or exposed to sunlight through windows. The hardcoats protect the plastics from scratches and abrasion. The coatings also contain UV absorbers to shield the plastic from sunlight, helping to prevent photodegradation and coloring. The coatings may also protect the plastics from solvents, acids or bases.
Ultraviolet light (i.e. radiation curable) curable abrasion resistant coating compositions contain acrylate monomers and oligomers which can be cured using a free radical type of photoinitiator. For greater abrasion resistance, the coatings may contain nanoparticles functionalized to disperse in the coating. The ultraviolet radiation-cured coating compositions are advantageous because of their short curing times. These coatings provide increased weatherability, or abrasion resistance or a combination of weatherability and abrasion resistance to the underlying thermoplastic substrate.
Ultraviolet radiation-curable abrasion-resistant coatings are known in the art. U.S. Pat. No. 4,455,205 discloses compositions comprising a silyl acrylate, aqueous colloidal silica, a photoinitiator and optionally a polyfunctional acrylate. Other types of ultraviolet radiation-curable coating compositions are disclosed in U.S. Pat. Nos. 4,486,504; 4,491,508; and 5,162,390
U.S. Pat. Nos. 5,571,570; 5,990,188; 6,087,413: 6,110,988; and 6,998,425 disclose weatherable, UV curable coating compositions containing urethane acrylate oligomers and UV absorbers.
In view of the increasingly stringent outdoor weathering conditions that thermoplastic substrates, such as polycarbonates, are being subjected to, the coatings manufacturing community has a need for further enhancements in regard to durability and weatherability. The present invention provides one answer to that need.